The diversity of molluscan faunas in marine lakes of Raja Ampat, West Papua, Indonesia

Abstract Marine lakes are bodies of seawater that are land-locked and maintain a subterranean connection to the surrounding sea. Here, we document the species diversity of benthic molluscs in 11 marine lakes in Raja Ampat, West Papua, Indonesia, using the roving diving survey method. We specifically tested for relationships between species richness and lake size and the degree of connection to the surrounding sea, and tested potential environmental drivers of community structure. We recorded 73 species, belonging to the classes Gastropoda (48 species, comprising 36 genera and 25 families), Bivalvia (24 species, consisting of 17 genera and 12 families), and Polyplacophora (one species). Molluscs from marine lakes are a subset of species also occurring in coral, seagrass, mangrove, and rocky shore habitats in the open sea. We found lake communities to mostly consist of grazers and filter feeders. The number of mollusc species significantly increased with increasing connection to the surrounding sea, but not with increasing surface area, indicating that dispersal potential may be the main driving force. Furthermore, we observed no significant influence of the environment on the variation in mollusc species composition among marine lakes. Still, we observed certain species to be exclusively present in either high or low-connected lakes, indicating a potential effect of environmental filtering. Marine lakes provide a unique ecosystem for diverse mollusc assemblages and as such should be protected.